Road Milling Machine And Method For Measuring The Milling Depth

ABSTRACT

A method is provided for measuring the milling depth of a road milling machine, the machine being operative to mill a ground surface with a milling roller lowered to a milling depth to create a milling track, the machine including at least one side plate located to at least one side of the milling roller to engage an untreated ground surface, and the machine including a stripping plate operative to be lowered onto the milling track generated by the milling roller. The method includes measuring the milling depth of the milling track, the measuring including detecting a measurement value of a ground engaging sensor engaging the milling track.

RELATED APPLICATIONS

The present application claims the priority of the German PatentApplication No. 10 2006 062 129.8 of Dec. 22, 2006, the disclosure ofwhich is herewith incorporated herein by reference. This application isalso a divisional of U.S. patent application Ser. No. 12/003,094 filedDec. 20, 2007, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention refers to a self-propelled road milling machine,especially a cold milling machine, as well as a methods for measuringthe milling depth.

2. Description of Related Art

With such road milling machines, the machine frame is supported by atrack assembly comprising wheels or caterpillar tracks connected to themachine frame through lifting columns, the lifting columns allowing tomaintain the machine frame in a horizontal plane or in parallel to theground or under a predetermined longitudinal and/or transversalinclination.

A milling roll for working a ground or traffic surface is supported atthe machine frame.

Near the front end sides of the milling roll height-adjustable sideplates are provided as edge protectors at an outer wall of the roadmilling machine, which side plates, in operation, rest on the ground ortraffic surface at the lateral non-milled edges of the milling track.Behind the milling roll, seen in the travelling direction, aheight-adjustable stripping means is provided which, in operation, maybe lowered into the milling track formed by the milling roll to stripoff milling material remaining in the milling track. Further, the roadmilling machine has a control means for controlling the milling depth ofthe milling roll.

It is a problem with known road milling machines that the milling depthcan not be controlled accurately enough and that, for this reason, themilling depth has to be measured repeatedly by hand during the millingoperation. Especially in cases where a hard traffic surface, e.g.concrete, is milled, the tools are worn heavily so that the millingdepth set is corrupted by the decreasing diameter of the cutting circle.For example, the wear of the tools, when milling concrete, can cause adifference in the milling radius of 15 mm after only a few 100 m, sothat the measuring of an adjustment of side plates, for example, withrespect to the machine frame is not sufficiently accurate. If themilling depth is insufficient, a time-consuming reworking of the millingtrack has to be carried out. Should the milling track be too deep, morebuilding material has to be applied afterwards in order to achieve thedesired ground or traffic surface level.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the accuracy ofmeasuring the milling depth during the operation of a road millingmachine and to thereby minimize deviations from a predetermined millingdepth.

The invention advantageously provides that at least one measuring meansdetects the lifting of a first sensor means resting on the ground ortraffic surface and/or the lowering of a second sensor means to thebottom of the milling track, the lifting or lowering being effected incorrespondence with the present milling depth. From the measured valuessupplied by the at least one measuring means, the control means candetermine the milling depth at the level of the measuring means of themilling roll or the second sensor means.

Here, the measurement is effected preferably at the level of thestripping means arranged closely behind the milling roll, or immediatelybehind the stripping means, if a separate sensor means is provided.

Using the stripping means as a sensor means is advantageous in that nomeasuring errors are caused by some unevenness in the milling track. Itis another advantage that the stripping means is protected against wearat its bottom edge.

As an alternative, the control means can use the measurement values ofthe at least one measuring means to determine the current milling depthof the milling roll at the level of the milling roll axis. Preferably,this is done by a calculation that may also take into account aninclined position of the machine frame.

The measuring means are preferably formed by position sensing means. Inone embodiment it is provided that the first sensor means is formed byat least one of the side plates arranged on either side at the frontsides of the milling roll so as to be height-adjustable and pivotablewith respect to the machine frame. The side plates rest on the ground ortraffic surface or are pressed against these, so that a change of theirposition relative to the machine frame during operation allows for anexact detection of the milling depth, if a measurement of the change ofthe position of a second sensor means is performed additionally in themilling track relative to the machine frame.

Also for side plates, there is an advantage that their bottom edges areprotected against wear.

Here, the measuring means may comprise cable lines coupled with the sideplates and/or the stripping means, and associated cable-line sensors asthe position sensors which measure the changes of the position of theside plates and the stripping means relative to the machine frame or therelative displacement of at least one of the side plates in relation tothe stripping means or the second sensor means.

Preferably, the cable lines coupled with the side plates and thestripping means are arranged transversely to the milling track in asubstantially vertical plane extending approximately at the level of thestripping means.

Hereby, it can be avoided that a measurement error is caused by usingdifferent reference planes for the measurement at the side plates withrespect to the measurement at the stripping plate.

To achieve this, it may be provided that a cable line is coupled on theone hand with the stripping means and, on the other hand, with at leastone of the side plates via a guide roller, such that a cable-line sensorimmediately measures the milling depth, e.g. at the guide roller.

In another alternative it may be provided that the side plate has arespective measuring means at the side edges facing the side plates,which measures the relative displacement of the stripping means withrespect to the at least one adjacent side plate or the relativedisplacement of at least one side plate with respect to the strippingmeans.

According to another alternative embodiment, the stripping means mayinclude at least one height-adjustable beam as the first sensing means,which is guided vertically and linearly in the stripping means andextends transversely to the travelling direction, said beam resting onthe ground or traffic surface beside the milling track, the position ofthe beam relative to the stripping means, preferably with respect toheight and/or inclination, being measurable by the measuring means.

Due to gravity, the side plates may rest on the edges of the ground ortraffic surface beside the milling track milled by the milling machine,or they may alternatively be pressed on the edges by hydraulic means.

The stripping means may also be pressed on the surface of the millingtrack using hydraulic means.

The hydraulic means for pressing the side plates on the ground ortraffic surface or for pressing the stripping means on the bottom of themilling track may comprise integrated position sensing systems.

For lifting or lowering the side plates and/or the stripping means, aplurality of, preferably two respective piston/cylinder units withintegrated position sensing systems may be provided, whose positionsensing signals are used by the control means to calculate the currentmilling depth from the relative difference between the positions of thestripping means and the at least one first sensor means.

The control means that receives the position sensing signals from themeasuring means is adapted to automatically control the lifted conditionof the rear lifting columns, seen in the travelling direction, toestablish parallelism between the machine frame and the ground ortraffic surface at a desired milling depth.

The side plates resting on the traffic surface so as to be pivotablewith respect to the machine frame may comprise measuring means spacedapart in the travelling direction, the control means being capable tomeasure the longitudinal and/or the transversal inclination of themachine frame with respect to the ground or traffic surface from thedifference between the measurement signals from the side plates and thestripping means.

The front and/or rear lifting columns may include a position sensingsystem to detect the lifted condition. The control means that receivesthe position sensing signals from the measuring means can control thecondition of all lifting columns such that the machine frame has apredetermined inclination or a predetermined travel-distance-dependenttransverse inclination across the travelling direction.

Preferably, the current set value for the milling depth of the millingroll is adjusted using the front lifting columns.

The following is a detailed description of a preferred embodiment of theinvention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cold milling machine.

FIG. 2 illustrates a first sensor means attached to the stripping plate.

FIG. 3 shows two piston/cylinder units for lifting or lowering thestripping plate of a stripping means.

FIG. 4 illustrates an optical device for measuring the positionaldifference between the side plates and the stripping means.

FIG. 5 shows a cable line measuring means provided between the sideplates and the stripping means.

FIG. 6 illustrates a preferred embodiment.

FIGS. 7 a, b, c are schematic illustrations of the measurement erroroccurring at the stripping plate of the stripping means in the absenceof parallelism between the machine frame and the ground or trafficsurface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The road milling machine illustrated in FIG. 1 comprises a machine frame4 supported by a track assembly having two front chain tracks 2 and atleast one rear chain track 3. The chain tracks 2, 3 are connected withthe machine frame 4 via lifting columns 12, 13. It is understood thatwheels may be used instead of the chain tracks 2, 3.

Using the lifting columns 12, 13, the machine frame 4 can be lifted orlowered or moved to take a predetermined inclined position with respectto the ground or traffic surface 8. The milling roll 6 supported in themachine frame 4 is enclosed by a roll case 9 which is open at the front,seen in the travelling direction, towards a conveyor belt 11 thatconveys the milled material in a front part of the machine frame 4 to asecond conveyor means 13. The second conveyor means 13 with which themilled material may be delivered onto a truck, for example, is not fullyillustrated in FIG. 1 because of its length. Behind the milling roll 6,a height-adjustable stripping means 14 is arranged which, in operation,has a stripping plate 15 engage into the milling track 17 formed by themilling roll 6 and strip the bottom of the milling track 17 so that nomilled material is left in the milling track 17 behind the strippingplate.

Above the milling roll 6, a driver's stand 5 with a control panel forthe vehicle operator is provided for all control functions of thedriving and milling operations. It also includes a control means 23 forcontrolling the milling depth of the milling roll 6.

The side plates 10, arranged on either side near the front end of themilling roll 6, and the stripping means 14 are provided with measuringmeans 16 that allow the determination of the current milling depth atthe level of the stripping means 14 or the calculation of the millingdepth at the level of the rotational axis of the milling roll. Here, themilling depth is determined in a plane orthogonal to the ground ortraffic surface, which plane is parallel to the rotational axis of themilling roll and includes the rotational axis.

The position of a first sensor means, e.g. the side plates 10, on theground or traffic surface 8 and/or the lowering of a second sensormeans, e.g. the stripping means, can thus be detected. Measuring means16, preferably formed by position sensing means, measure thedisplacements of the sensor means, e.g. the side plates 10 or a beam 20or the stripping plate 15, with respect to the machine frame 4 orrelative to each other.

The embodiment illustrated in FIG. 2 shows a beam 20 as the sensormeans, resting on the ground or traffic surface 8 and guided at thestripping plate 15 of the stripping means in a slot 24 extendinglinearly and orthogonally to the bottom edge 19 of the stripping plate15. It is understood that two mutually parallel slots 24 can be providedin the stripping plate 15 or that the beam 20, serving as the sensingmeans, can be guided in a different manner so as to be height-adjustableat the stripping means 14. The measuring means 16, provided in the formof a position sensing means, detects the displacement of the beam 20with respect to the stripping means 14. Should two horizontally spacedslots 24 be used, it is possible to separately detect the milling depthon the left side of the milling track 17 and on the right side of themilling track 17. Moreover, this offers the possibility to determine aninclination of the machine frame 4 with respect to the ground or trafficsurface 8.

FIG. 3 illustrates another embodiment wherein the stripping plate 15 ofthe stripping means 14 can be lifted or lowered by means of hydraulicmeans. The hydraulic means are formed by piston/cylinder units 26, 28with an integrated position sensing system. This means that thepiston/cylinder units 26, 28 not only allow for the stroke movement ofthe stripping means, but moreover generate a position signal.

As is evident from FIG. 3, the piston/cylinder units 26, 28 have one endconnected to the machine frame 4 and the other end connected to thestripping plate 15.

FIG. 4 illustrates an embodiment, wherein the relative movement betweenthe side plates 10 and the stripping plate 15 is measured directly inorder to detect the milling depth of the milling track 17. To achievethis, elements 38, 40 of the measuring means 16 are provided, e.g., atthe side plates 10 and opposite thereto at the stripping plate 15, whichelements allow for the detection of the relative displacement of thestripping plate 15 with respect to the side plates 10. This displacementcorresponds to the milling depth s in FIG. 4. For example, such ameasuring means, which measures relative displacements, may be formed byan optical system, e.g. by reading a scale with an optical sensor, or byan electromagnetic or inductive system.

As an alternative and as illustrated in FIG. 5, the relative positionsensing system between the side plates 10 and the stripping plate 15 mayalso be formed by a cable line 22 in combination with a cable-linesensor 21. the cable line 22 is coupled with the stripping plate 15 ofthe stripping means 14 on the one hand and, on the other hand, with atleast one of the side plates 10 via a guide roller 35, so that thesignal from the cable-line sensor 21 can immediately indicate the valueof the current milling depth.

The side plates 10 themselves can be used as first sensor means bymonitoring their position with respect to the machine frame 4 or thesecond sensor means by means of a cable line and a cable-line sensor orby means of piston/cylinder units 30, 32 with integrated positionsensing means.

For example, the measuring means can also measure the displacement ofthe side plates 10 with respect to the machine frame 4. Should twomeasuring means be used, one in front of the side plates 10 and onebehind the same, seen in the travelling direction, it is also possibleto determine the longitudinal inclination of the machine frame 4 withrespect to the ground or traffic surface 8 or to also determine thetransverse inclination of the machine frame 4 by a comparison of themeasured values for both side plates 10 on both sides of the millingroll 6.

FIG. 6 illustrates a preferred embodiment, wherein cable lines 22comprising cable-line sensors 21 mounted to the machine frame 4 arearranged on both sides of the stripping means 15. On either side of themachine, the side plates 10 are also provided with cable lines 22 andcable-line sensors 21 fastened at the machine frame 4. The milling depths is determined from the difference between the measured values of thecable-line sensors 21 for the side plates 10 and the cable-line sensors21 of the stripping means 15. Here, the measurement should preferably bemade in the same substantially vertical plane in order to avoidmeasurement errors.

FIGS. 7 a to 7 c illustrate the cable-line sensors 21 for the sideplates 10 and the stripping plates 14, the drawings only indicating onecable-line sensor 21, since the cable-line sensors are arranged onebehind the other in substantially the same plane.

FIGS. 7 a, b, c are to illustrate the case where the ground or trafficsurface 8 is not parallel to the machine frame 4, the measured millingdepth value indicated by the measuring means having to be correctedbecause of an angle error, because a longitudinal inclination of themachine frame 4 corrupts the measurement signal at the level of thestripping plate 15 or a second sensor means near the stripping means 14.Due to the fixed geometrical relations, i.e. the distance of thestripping plate 15 from the rotational axis of the milling roll 6, themeasured milling depth value can be corrected, knowing the angulardeviation from the horizontal in the travelling direction, and thecurrent milling depth at the level of the milling roll axis can becalculated. The angular deviation in the travelling direction may bedetermined, for example, from the position of the lifting columns 12, 13of the caterpillar track assemblies 2, 3 or the piston/cylinder units30, 32.

It is further evident from FIGS. 7 a to c, to which extent the sideplates 10 are pivotable with respect to the machine frame 4. Since thepiston/cylinder units 30, 32 are also provided with position sensingsystems, these measuring signals may be used as an alternative tocable-line sensors 21 to determine the distance of the side plates 10from the machine frame 4.

FIG. 7 c illustrates the position of the at least one side plate 10 fora ground-parallel position of the machine frame 4. The stripping plate15 illustrated in FIGS. 7 a to 7 c is located at the roll case 9, sothat the distance of the stripping plate 14 from the rotational axis tothe milling roll 6 can be determined unambiguously in order to allow fora calculation of the milling depth correction should the machine frame 4not be parallel to the ground.

The control means 23 can calculate the current milling depth at thelevel of the milling roll axis from the position sensing signalsreceived, and it can possibly also generate a control signal for avertical adjustment of the milling roll 6.

Preferably, the control means 23 can automatically control the liftedcondition of the at least one rear lifting column 13, seen in thetravelling direction, to establish parallelism between the machine frame4 and the ground or traffic surface 8 or to the horizontal plane or to apredetermined desired milling plane.

Although the invention has been described and illustrated with referenceto specific embodiments thereof, it is not intended that the inventionbe limited to those illustrative embodiments. Those skilled in that artwill recognize that variations and modifications can be made withoutdeparting from the true scope of the invention as defined by the claimsthat follow. It is therefore intended to include within the inventionall such variations and modifications as fall within the scope of theappended claims and equivalents thereof.

1. A method for measuring the milling depth of a road milling machine,the machine being operative to mill a ground surface with a millingroller lowered to a milling depth to create a milling track, the machineincluding at least one side plate located to at least one side of themilling roller to engage an untreated ground surface, and the machineincluding a stripping plate operative to be lowered onto the millingtrack generated by the milling roller, the method comprising: measuringthe milling depth of the milling track, the measuring includingdetecting a measurement value of a ground engaging sensor engaging themilling track.
 2. The method of claim 1, wherein: the ground engagingsensor engaging the milling track includes the stripping plate.
 3. Themethod of claim 1, wherein: the measuring step further includesdetecting another measurement value of another ground engaging sensorengaging the untreated ground surface, and wherein both measurementvalues are detected in relation to a machine frame of the road millingmachine.
 4. The method of claim 3, wherein: the other ground engagingsensor engaging the untreated ground surface includes the side plate. 5.The method of claim 4, wherein: the ground engaging sensor engaging themilling track includes the stripping plate.
 6. The method of claim 1,wherein: the measuring step further includes detecting the measurementvalue of the ground engaging sensor engaging the milling track inrelation to another ground engaging sensor engaging the untreated groundsurface.
 7. The method of claim 1, further comprising: correcting themeasured milling depth in dependence on an offset distance between theground engaging sensor engaging the milling track and a rotational axisof the milling roller, when the machine frame does not extend parallelto the untreated ground surface.
 8. A method of controlling aself-propelling road milling machine, the milling machine including amachine frame, a milling roller supported from the frame for treatmentof a ground surface, at least one height adjustable side plate arrangedto at least one side of the milling roller, and a height adjustablestripping plate arranged behind the milling roller, wherein the methodcomprises: (a) engaging the ground surface to be treated with a firstground engaging sensor, and sensing with the first ground engagingsensor a first signal corresponding to a first distance of the machineframe from the ground surface to be treated; and (b) engaging themilling track with the stripping plate, and sensing with a second sensorconnected to the stripping plate a second signal corresponding to asecond distance of the machine frame from the milling track.
 9. Themethod of claim 8, further comprising: determining with a controller amilling depth of the milling roller from the first and second signals.10. The method of claim 8, wherein: in step (a) the first groundengaging sensor includes the height adjustable side plate.
 11. Themethod of claim 10, further comprising: resting the side plate under theeffect of gravity on an un-milled portion of the ground surface adjacentan edge of the milling track.
 12. The method of claim 10, furthercomprising: pressing the side plate onto an un-milled portion of theground surface adjacent an edge of the milling track with a hydraulicpiston/cylinder unit.
 13. The method of claim 10, wherein: in step (a)the height adjustable side plate includes a hydraulic piston/cylinderunit for height adjustment, and first sensor comprises an integratedposition sensor contained in the hydraulic piston/cylinder unit.
 14. Themethod of claim 8, further comprising: pressing the stripping plate ontothe milling track with a hydraulic piston/cylinder unit.
 15. The methodof claim 14, wherein: in step (b) the second sensor comprises anintegrated position sensor contained in the hydraulic piston/cylinderunit.
 16. The method of claim 8, wherein the road milling machineincludes front and rear lifting columns supporting the machine framefrom front and rear ground engaging supports, each of the liftingcolumns including a position sensing device to detect a lifting positionof its associated lifting column, the method further comprising:controlling with a controller a milling depth of the milling roller bycontrolling the lifting positions of the lifting columns.
 17. The methodof claim 8, wherein the road milling machine includes at least two frontground engaging supports, at least one rear ground engaging support, andfront and rear lifting columns supporting the machine frame from theground engaging supports, the front lifting columns each including aposition sensing device configured to detect a lifting position of itsassociated lifting column, the method further comprising: controllingwith a controller a milling depth of the milling roller by controlling alifting condition of the front lifting columns.
 18. The method of claim8, further comprising: prior to step (b), setting a zero level for amilling depth of the milling roller when the first and second sensorsare engaged with an un-milled ground surface.
 19. The method of claim 8,wherein: in step (b), the second sensor comprises a cable line coupledto the stripping plate as a position sensing device.
 20. The method ofclaim 8, wherein: in step (a), the first sensor comprises a cable linecoupled to the side plate as a position sensing device.